Butterfly valves are the most widely used among all valves, as they are compact and light weight with good performing characteristics in low to middle pressure ranges. One shortcoming of the conventional butterfly valve is its less than acceptable shut-off performance. With few exceptions, the conventional butterfly valves employ a disc squeezably engaging a valve seat made of a resilient material. Since the rim of the valve disc and the resilient valve seat included in conventional butterfly valves experience a rubbing and scraping action constantly during the opening and closing thereof, they are prone to wear and tear that results in leaks. In applications subjected to high temperatures or highly corrosive environments, the use of resilient materials for the valve seat is often not compatible, and, consequently, conventional butterfly valves have severe limitations as far as their use as specialty valves.
The primary object of the present invention is to provide a floating disc butterfly valve wherein the valve disc is movable over a small distance from or to the valve seat, which movement of the disc is created by a small amount of axial movement of the valve stem.
Another object is to provide a floating disc butterfly valve having a substantially spherical valve seat and a substantially spherical valve disc rim.
A further object is to provide a floating disc butterfly valve with a valve disc mechanically connected to a valve stem supported at both ends.
Yet another object is to provide a floating disc butterfly valve with a valve disc mechanically connected to a pair of cantilever valve stems.
Yet a further object is to provide a butterfly valve that includes a valve seat made of a hard material constituting the valve body.
Still another object is to provide a butterfly valve that includes a valve disc with an annular seal made of a hard or resilient material disposed in the rim of the valve disc.
Still a further object of the present invention is to provide a butterfly valve providing one hundred percent shut-off.
Additionally another object is to provide a butterfly valve wherein the valve seat and the rim of the valve disc are not subjected to mechanical abrasion during opening and closing of the valve.
Additionally a further object is to provide a butterfly valve compatible with extreme working environments such as high temperature, cryogenic and highly corrosive applications.
These and other objects of the present invention will become clear as the description thereof proceeds.